1. Field of the Invention
The present teaching relates to a method for sorting a reusable nonaqueous electrolyte secondary battery from spent nonaqueous electrolyte secondary batteries. The present application claims priority to Japanese Patent Application No. 2015-171348 filed on Aug. 31, 2015, the entire contents of which are hereby incorporated by reference.
2. Description of the Related Art
Nonaqueous electrolyte secondary batteries such as lithium ion secondary batteries have been used in recent years as the so-called portable power sources for personal computers, portable terminals, and the like, and as drive power sources for vehicles. When nonaqueous electrolyte secondary batteries are used as a drive power source for vehicles, they are used as a battery pack in which a plurality of nonaqueous electrolyte secondary batteries (unit batteries) are electrically connected to each other. Accordingly, the demand for nonaqueous electrolyte secondary batteries has been steadily growing.
Nonaqueous electrolyte secondary batteries that have reached a service life need to be replaced, and as the demand for the batteries grows, the number of spent nonaqueous electrolyte secondary batteries is expected to rise. Accordingly, from the standpoint of efficiently reusing the resources and reducing the running cost, it is necessary to establish a method for accurately determining whether a battery can be reused by accurately detecting the degradation state of spent nonaqueous electrolyte secondary batteries. In this respect, for example, Japanese Patent Application Publication No. 2014-020818 discloses the feature of using the open circuit voltage value, internal resistance value, and full charge capacity value of each of the batteries constituting a battery pack, as indicators for determining the reusability of the nonaqueous electrolyte secondary batteries.